The invention relates to a spiral link belt with a plurality of helices connected to one another, whereby the windings of neighboring helices are fitted into one another in the manner of a slide fastener, with the result that the overlapping winding zones form a channel. Pintle wires run in the channels, with the result that the helices cannot be separated. To reduce the permeability of the spiral link belt to air, flat wires are inserted as filling material into the free space of the helices. The invention also relates to a method for the production of such a spiral link belt.
Such spiral link belts are used in particular in the drier section of high-speed paper machines. To achieve a low permeability to air, it is necessary to fill the free inside space of the helices with filling material. If the permeability to air is too great, the spiral link belt creates a very strong turbulent air flow which can lead to uneven running and even to the breakage of the paper web. Spiral link belts currently in use still have a permeability to air of at least 2280 m.sup.3 /m.sup.2 /hr/100 Pa (CFM 140). This is too high for many applications.
Spiral link belts in which the free space inside the helices is filled with filling material in order to reduce the permeability to air are disclosed in U.S. Pat. No. 4,362,776 and U.S. Pat. No. 4,564,992. The filling material can consist, inter alia, of a strip of yarn or of a flat strip.
A spiral link belt with flat wires as filling material is disclosed in U.S. Pat. No. 4,381,612. Instead of a single flat wire, two filling threads can also be inserted into the free space of every helix.
Also disclosed is a version in which filling wires made from material with a low melting point, e.g. nylon or polypropylene, are used. Upon thermosetting, these filling wires then melt and close the open meshes of the spiral link belt.
Spiral link belts are produced by fitting the helices into one another first and then inserting pintle wires into the channels which the overlapping windings of neighboring helices form. If a spiral link belt with as low as possible permeability to air is to be produced, filling wires are subsequently inserted into the free inside space of the helices. When flat wires are used as filling wires, precautions must be taken to ensure that the flat wires do not become twisted. If several round wires are inserted as filling material into the inside space of every helix, it must be ensured that the round wires do not lie above one another. The result of a twisting of the flat wires or of a superimposition of the round wires is that the monoplanar character of the finished spiral link belt is destroyed, which can lead to markings in the paper web. This problem is usually countered by pre-setting the spiral link belt before the insertion of the filling wires and, in so doing, flattening the originally slightly oval cross-section shape of the helices by means of heat and pressure to the extent that the flat wires and the several round wires can no longer become twisted or superimposed on one another. After the insertion of the filling wires, the spiral link belt then undergoes final thermosetting. The pre-setting is thus an additional work step which causes substantial costs.
With the known spiral link belts, the filling wires also lie relatively loosely in the inside of the helices. It is true that the edges of a spiral link belt are glued, whereby the lateral openings of the helices are closed, with the result that the filling wires cannot slip out sideways. However, the edges of a spiral link belt are often damaged while running in the paper machine and the filling wires pulled out.